Material "Base Color" doesn't change when "Use Nodes" selected
You probably have the solid display button on and haven't pressed the render button.  In the video you mention there are several buttons at the top right of the 3d viewport that are associated with overlays and displays like wireframe, solid, lookdev, render, and shading -- note that the render button, just to the left of the shading drop down menu, is turned on.  BY the way, on my 2.8 beta version all those buttons are at the bottom right of the 3d viewport.